Heretofore unauthorized use of expensive, delicate or dangerous electrical equipment and machinery has been prevented by traditional lock-and-key devices such as taught in United States Letter Patents:
U.S. Pat. No. 2,654,037 issued Sept. 29, 1953 to Katz, PA0 U.S. Pat. No. 4,488,764 issued Dec. 18, 1984 to Pfenning, PA0 U.S. Pat. No. 4,592,607 issued June 3, 1986 to Pejovie, and PA0 U.S. Pat. No. 4,648,667 issued Mar. 10, 1987 to Baumgart.
The plug on the cord to the electrical equipment was placed in a strong, tamper proof container which was then closed and secured shut by a lock.
The key was available to authorized personnel only. Unauthorized personnel were unable to open the container, and were prevented from using the secured device unless they had possession of the key. Mere verbal permission from the authorized personnel was insufficient. The key had to be located and brought to the equipment location. Without keys, unauthorized personnel were unable to exercise discretion in emergencies or other unforeseeable situations.
A second disadvantage of these lock-and-key devices concerned the long lifetime of the lock mechanism. Over the years many extra keys were made, and unauthorized personnel eventually possessed unauthorized keys. The security of the lock-and-key devices became diluted.
U.S. Pat. No. 4,219,693 issued Aug. 26, 1980 to French teaches a security technique which discourages unauthorized use of electronic equipment; but does not physically prevent unauthorized use. The input cable to the electronic device was secured within a brittle plastic shell. The shell was formed by opposed halves which snap together around the cable to prevent use. The shell had to be broken and removed in order to install the cable and use the equipment. A missing shell, or pieces of a broken shell, indicated unauthorized use. The fear of post use detection discouraged tampering by unauthorized individuals.